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Recursos presión

Unidades de presión

Se introducen unidades (Pa, atm, bar, mmHg)

Aparte de Pa (pascal), hay otras aceptadas por el SI

Table 8. Other non-SI units
 Quantity Name of unit  Symbol for unit  Value in SI unit
 pressure bar (a)bar  1 bar = 0.1 MPa = 100 kPa = 105 Pa 
  millimetre of mercury (b)mmHg 1 mmHg ≈ 133.322 Pa

(a) The bar and its symbol are included in Resolution 7 of the 9th CGPM (1948; CR, 70). Since 1982 one bar has been used as the standard pressure for tabulating all thermodynamic data. Prior to 1982 the standard pressure used to be the standard atmosphere, equal to 1.013 25 bar, or 101 325 Pa. 

(b) The millimetre of mercury is a legal unit for the measurement of blood pressure in some countries. 

La atmósfera

Una atm son 101325 Pa (en libro de texto reciente veo que indica 101300 Pa, y son 101235 Pa desde 1954)
1 standard atmosphere = 1 013 250 dynes per square centimetre, i.e., 101 325 newtons per square metre.

In 1954, the definition of the atmosphere was revised by the 10e Conférence Générale des Poids et Mesures (10th CGPM)[https://www.bipm.org/en/CGPM/db/10/4/] to the currently accepted definition: one atmosphere is equal to 101325 pascals. The torr was then redefined as 1/760 of one atmosphere. This yields a precise definition that is unambiguous and independent of measurements of the density of mercury or the acceleration due to gravity on Earth.

Milímetros de mercurio

El símbolo es mmHg según SI:  junto, no separado.
Se puede usar torr (nombre torr, símbolo Torr), pero se desaconseja

Table 11. Example of other unacceptable units
 NameSymbol  Value in SI units
 torrTorr 1 Torr = (101 325/760) Pa 

The unit's name torr is written in lower case, while its symbol ("Torr") is always written with upper-case initial; including in combinations with prefixes and other unit symbols, as in "mTorr" (millitorr) or "Torr⋅L/s" (torr-litres per second).[2] The symbol (uppercase) should be used with prefix symbols (thus, mTorr and millitorr are correct, but mtorr and milliTorr are not).
The torr is sometimes incorrectly denoted by the symbol "T", which is the SI symbol for the tesla, the unit measuring the strength of a magnetic field. Although frequently encountered, the alternative spelling "Tor" is incorrect.

Presión estándar

Citado en apuntes de termoquímica de Bachillerato

Abbreviation for standard temperature (273.15 K or  0 °C) and pressure (105 Pa); usually employed in reporting gas volumes. Note that flow meters calibrated in standard gas volumes per unit time often refer to volumes at  25 °C, not  0 °C.